Bottom emission microLED display and a repair method thereof

ABSTRACT

A bottom emission microLED display includes a microLED disposed above a transparent substrate; a light guiding layer surrounding the microLED to controllably guide light generated by the microLED towards the transparent substrate; and a reflecting layer formed over the light guiding layer to reflect the light generated by the microLED downwards and to confine the light generated by the microLED to prevent the light from leaking upwards or sidewards.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 16/405,891, filed on May 7, 2019, and now allowed, which in turn isa divisional application of U.S. application Ser. No. 15/963,477, filedon Apr. 26, 2018, now abandoned, which in turn claims priority to TaiwanPatent Application No. 106114691, filed on May 3, 2017. The entirecontents of each of the foregoing applications are herein expresslyincorporated by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention generally relates to a micro light-emitting diode(microLED), and more particularly to a bottom emission microLED displayand a repair method thereof.

2. Description of Related Art

A micro light-emitting diode (microLED, mLED or μLED) display panel isone of flat display panels, and is composed of microscopic microLEDseach having a size of 1-10 micrometers. Compared to conventional liquidcrystal display panels, the microLED display panels offer bettercontrast, response time and energy efficiency. Although both organiclight-emitting diodes (OLEDs) and microLEDs possess good energyefficiency, the microLEDs, based on group III/V (e.g., GaN) LEDtechnology, offer higher brightness, higher luminous efficacy and longerlifespan than the OLEDs.

During manufacturing a microLED display panel, individual microLEDsshould be picked up and transferred to a display panel by electrostaticforce, magnetic force or vacuum suction force. In practice, whileperforming picking, transferring and bonding, some individual microLEDsmay be picked up and released abnormally, or the microLEDs aredefective. After the microLEDs are bonded with a substrate of thedisplay panel, it is difficult to repair those microLEDs that aredefective or cannot be operated normally. A destructive scheme isusually adopted to perform the repairing, which is complicated andtime-consuming.

A need has thus arisen to propose a simple and fast scheme to repair amicroLED display panel.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the embodiment of thepresent invention to provide a bottom emission microLED display and arepair method thereof. The repair method of the microLED display canrepair the microLED display fast and conveniently without usingdestructive scheme.

According to one embodiment, a bottom emission micro light-emittingdiode (microLED) display includes a transparent substrate, a microLED, alight guiding layer and a reflecting layer. The microLED is disposedabove the transparent substrate. The light guiding layer surrounds themicroLED to controllably guide light generated by the microLED towardsthe transparent substrate. The reflecting layer is formed over the lightguiding layer to reflect the light generated by the microLED downwardsand to confine the light generated by the microLED to prevent the lightfrom leaking upwards or sidewards.

According to a repair method of a bottom emission micro light-emittingdiode (microLED) display of one embodiment, a transparent substrate isprovided with an original area and a repair area. A first conductivelayer is formed to result in a selection electrode and an extendedelectrode extended from the selection electrode towards the repair area.A vertical-type original microLED is disposed above the selectionelectrode, which bonds and electrically connects with a first electrodeof the microLED. A first light guiding layer is entirely formed abovethe transparent substrate, the selection electrode, the extendedelectrode and the original microLED. The first light guiding layer isetched to expose a second electrode of the original microLED and thetransparent substrate in the repair area. A second conductive layer isformed to result in a common electrode above the first light guidinglayer in the original area, thereby electrically connecting with thesecond electrode of the original microLED, and to result in the secondconductive layer above the exposed transparent substrate in the repairarea, wherein the extended electrode and the second conductive layer inthe repair area partially overlap. When the original microLED passes afunctional test, the following steps are performed: forming entirely asecond light guiding layer above the common electrode and the firstlight guiding layer; etching the second light guiding layer to exposethe common electrode and forming a top electrode above the second lightguiding layer to electrically connect with the common electrode. Whenthe original microLED fails the function test, the following steps areperformed: disposing a vertical-type repair microLED on the secondconductive layer above the exposed transparent substrate in the repairarea, such that a first electrode of the repair microLED bonds andelectrically connects with the second conductive layer above the exposedtransparent substrate; welding to electrically connect the partiallyoverlapped second conductive layer and the extended electrode; formingentirely the second light guiding layer above the repair microLED, thecommon electrode in the original area and the first light guiding layer;and etching the second light guiding layer to expose the commonelectrode and a second electrode of the repair microLED, and forming thetop electrode above the second light guiding layer to electricallyconnect the common electrode and the second electrode of the repairmicroLED.

According to a repair method of a bottom emission micro light-emittingdiode (microLED) display of another embodiment, a transparent substrateis provided. A selection electrode is formed above the transparentsubstrate. A first insulating layer is formed above the transparentsubstrate and the selection electrode. A through hole is formed in thefirst insulating layer. A conductive layer and a common electrode areformed above the first insulating layer, the conductive layer fillingthe through hole and thus electrically connecting with the selectionelectrode. A flip-chip type original microLED is disposed above theconductive layer and the common electrode such that a first electrode ofthe original microLED bonds and electrically connects with theconductive layer, and a second electrode of the original microLED bondsand electrically connects with the common electrode. When the originalmicroLED fails a functional test, a repair microLED is disposed abovethe conductive layer and the common electrode, such that a firstelectrode of the repair microLED bonds and electrically connects withthe conductive layer and a second electrode of the repair microLED bondsand electrically connects with the common electrode. The functional testand disposing a repair microLED are repeated until passing thefunctional test. A light guiding layer is formed above the firstinsulating layer, the conductive layer, the common electrode, theoriginal microLED and the repair microLED. A reflecting layer is formedabove the light guiding layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view illustrating a bottom emissionmicroLED display according to a first embodiment of the presentinvention;

FIG. 2 shows a cross-sectional view illustrating a bottom emissionmicroLED display according to a second embodiment of the presentinvention;

FIG. 3A to FIG. 3J show cross-sectional views illustrating a repairmethod of a bottom emission microLED display according to a thirdembodiment of the present invention;

FIG. 4 shows a partial top view illustrating the microLED display ofFIG. 3A to FIG. 3J;

FIG. 5A to FIG. 5F show cross-sectional views illustrating a repairmethod of a bottom emission microLED display according to a fourthembodiment of the present invention; and

FIG. 6 shows a partial top view illustrating the microLED display ofFIG. 5A to FIG. 5F.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a cross-sectional view illustrating a bottom emission microlight-emitting diode (microLED) display 100 according to a firstembodiment of the present invention. For better understanding theembodiment, only one microLED 11 or a pixel light-emitting area isshown. In the specification, the microLED 11 has a size of 1-10micrometers, which may be decreased or increased for specificapplications or according to future technology development.

The bottom emission microLED display 100 (“microLED display”hereinafter) may include a transparent substrate 12, which may, forexample, be made of glass or other non-conductive transparent material.An insulating layer 10 may be formed entirely above the transparentsubstrate 12. The insulating layer 10 may be an inter-layer dielectric(ILD) layer, which may include electrically insulating material such assilicon oxide or silicon nitride. A portion of the insulating layer 10may be etched to expose the transparent substrate 12. A selectionelectrode 13, which may include electrically conductive material such asmetal, may be formed on the exposed transparent substrate 12. As shownin FIG. 1, the microLED 11 is a vertical-type microLED with a firstelectrode 111 and a second electrode 112 that are disposed at bottom andtop of the microLED 11, respectively. Specifically, the first electrode111 bonds and electrically connects with the selection electrode 13. ThemicroLED display 100 may include a light guiding layer 14 that coversthe transparent substrate 12 and the microLED 11, thus surrounding themicroLED 11 to controllably guide light generated by the microLED 11towards the transparent substrate 12 such that the generated light maybe emitted downwards and be vertical to a top surface of the transparentsubstrate 12. In the embodiment, the light guiding layer 14 may be anover-coating (OC) layer, which may include transparent material withhigh refractive index (e.g., higher than 1.4) such as polymer (e.g.,polycarbonate (PC) or PolyMethyl MethAcrylate (PMMA)). The microLEDdisplay 100 may include a common electrode 15 covering the light guidinglayer 14 and electrically connecting with the second electrode 112 ofthe microLED 11. The common electrode 15 of the microLED display 100 asshown in FIG. 1 may also act as a reflecting layer to reflect the lightgenerated by the microLED 11 downwards and to confine the lightgenerated by the microLED 11 to prevent the light from leaking upwardsor sidewards. The common electrode 15 may include conductive materialsuch as metal (e.g., aluminum, molybdenum, copper, titanium ortungsten).

FIG. 2 shows a cross-sectional view illustrating a bottom emissionmicroLED display 200 according to a second embodiment of the presentinvention. Same numerals are used to denote elements that are the sameas FIG. 1.

The bottom emission microLED display 200 (“microLED display”hereinafter) may include a transparent substrate 12 with a selectionelectrode 13 formed thereon. The microLED display 200 may include aninsulating layer 16 covering the transparent substrate 12 and theselection electrode 13. In the embodiment, the insulating layer 16 maybe an inter-layer dielectric (ILD) layer, which may include electricallyinsulating material such as silicon oxide or silicon nitride. A commonelectrode 15 and a conductive layer 17 (including conductive materialsuch as metal) may be formed above the insulating layer 16. As shown inFIG. 2, the microLED 11 is a flip-chip type microLED with a firstelectrode 111 and a second electrode 112 disposed at bottom of themicroLED 11. Specifically, the first electrode 111 bonds andelectrically connects with the conductive layer 17, which furtherelectrically connects with the selection electrode 13; and the secondelectrode 112 bonds and electrically connects with the common electrode15. The microLED display 200 may include a light guiding layer 14 thatcovers the insulating layer 16 and the microLED 11, thus surrounding themicroLED 11 to controllably guide light generated by the microLED 11towards the transparent substrate 12 such that the generated light maybe emitted downwards and be vertical to a top surface of the transparentsubstrate 12. The microLED display 200 may include a reflecting layer 19covering the light guiding layer 14 to reflect the light generated bythe microLED 11 downwards and to confine the light generated by themicroLED 11 to prevent the light from leaking upwards or sidewards. Thereflecting layer 19 may include conductive material such as metal (e.g.,aluminum, molybdenum, copper, titanium or tungsten).

According to aspects of FIG. 1 and FIG. 2, the microLED display 100/200of the embodiment may include the transparent substrate 12 with themicroLED 11 disposed thereabove. The light guiding layer 14 surroundsthe microLED 11 to controllably guide light generated by the microLED 11towards the transparent substrate 12. The reflecting layer 19 covers thelight guiding layer 14 to reflect the light generated by the microLED 11downwards and to confine the light generated by the microLED 11 toprevent the light from leaking upwards and sidewards. The selectionelectrode 13 is disposed on the transparent substrate 12 andelectrically connects with the first electrode 111 of the microLED 11.For the vertical-type microLED 11 (FIG. 1), the reflecting layer acts asthe common electrode 15 and electrically connects with the secondelectrode 112 of the microLED 11. For the flip-chip type microLED 11(FIG. 2), the common electrode 15 is disposed between the microLED 11and the transparent substrate 12, and electrically connects with thesecond electrode 112 of the microLED 11.

FIG. 3A to FIG. 3J show cross-sectional views illustrating a repairmethod of a (bottom emission) microLED display 300 according to a thirdembodiment of the present invention. The embodiment is adaptable to avertical-type microLED. Same numerals are used to denote elements thatare the same as FIG. 1.

As shown in FIG. 3A, a transparent substrate 12 with an original area30A and a repair area 30B is provided. Only one repair area 30B of apixel light-emitting area is shown for brevity. Specifically, theoriginal area 30A is used for disposing an original microLED and therepair area 30B is used for disposing a repair microLED. An insulatinglayer 10 is formed entirely above the transparent substrate 12. Theinsulating layer 10 may be an inter-layer dielectric (ILD) layer, whichmay include electrically insulating material such as silicon oxide orsilicon nitride. A portion of the insulating layer 10 is etched toexpose the transparent substrate 12. Next, a first conductive layer(e.g., first metal layer) is formed on the exposed transparent substrate12, thereby resulting in a selection electrode 13A in the original area30A of the transparent substrate 12 as shown in FIG. 3A, which across-sectional view along a cross line 3A-3A′ of FIG. 4. An extendedelectrode 13B is extended from the selection electrode 13A towards therepair area 30B. The extended electrode 13B is shown in FIG. 3B, whichis a cross-sectional view along a cross line 3B-3B′.

The following descriptions refer to cross-sectional views along thecross line 3A-3A′ of FIG. 4 unless otherwise noted. Referring to FIG.3C, an original microLED 11A is disposed above the selection electrode13A in the original area 30A such that a first electrode 111A of theoriginal microLED 11A bonds and electrically connects with the selectionelectrode 13A. Next, a first light guiding layer 14A is formed toentirely cover the transparent substrate 12, the selection electrode13A, the extended electrode 13B and the original microLED 11A tocontrollably guide light generated by the original microLED 11A towardsthe transparent substrate 12 such that the generated light may beemitted downwards and be vertical to a top surface of the transparentsubstrate 12. In the embodiment, the first light guiding layer 14A maybe an over-coating (OC) layer, which may include transparent materialwith high refractive index (e.g., higher than 1.4) such as polymer(e.g., polycarbonate (PC) or PolyMethyl MethAcrylate (PMMA)).

As shown in FIG. 3D, the first light guiding layer 14A is etched toexpose a second electrode 112A of the original microLED 11A in theoriginal area 30A and expose the transparent substrate 12 in the repairarea 30B. Next, a second conductive layer (e.g., second metal layer) isformed, thus resulting in a common electrode 15 above the first lightguiding layer 14A in the original area 30A such that the commonelectrode 15 electrically connects with the second electrode 112A of theoriginal microLED 11A. Moreover, a second conductive layer 31 is alsoformed above the transparent substrate 12 in the repair area 30B. Thecommon electrode 15 in the original area 30A does not electricallyconnect with the second conductive layer 31 in the repair area 30B. FIG.3E shows a cross-sectional view along a cross line 3B-3B′ of FIG. 4,where the extended electrode 13B (in the repair area 30B) and the secondconductive layer 31 disposed thereabove partially overlap. Further, theexposed transparent substrate 12 (in the repair area 30B) is adjacent tothe extended electrode 13B.

After the structure of FIG. 3D/FIG. 3E is formed, the original microLED11A is subjected to functional test. If the original microLED 11A passesthe test, the process of FIG. 3F to FIG. 3G is performed; otherwise theprocess of FIG. 3H to FIG. 3J is performed.

As shown in FIG. 3F, if the original microLED 11A passes the functionaltest, a second light guiding layer 14B is entirely formed to cover thecommon electrode 15 and the first light guiding layer 14A. The secondlight guiding layer 14B in the repair area 30B is etched to expose thesecond conductive layer 31. In the embodiment, the second light guidinglayer 14B may be an over-coating (OC) layer, which may includetransparent material with high refractive index (e.g., higher than 1.4)such as polymer (e.g., polycarbonate (PC) or PolyMethyl MethAcrylate(PMMA)). The second light guiding layer 14B may be made of materialbeing the same as or different from the first light guiding layer 14A.

As shown in FIG. 3G, the second light guiding layer 14B is etched toexpose the common electrode 15 in the original area 30A. Next, a topelectrode 22 is formed above the second light guiding layer 14B toelectrically connect with the common electrode 15 in the original area30A. In the embodiment, the top electrode 22 may be a third metal layer.The top electrode 22 may be made of material being the same as ordifferent from the common electrode 15. Accordingly, the commonelectrode 15 and the top electrode 22 act to reflect the light generatedby the original microLED 11A downwards and to confine the lightgenerated by the original microLED 11A to prevent the light from leakingupwards or sidewards.

As shown in FIG. 3H, if the original microLED 11A fails the functionaltest, a repair microLED 11B is then disposed on the second conductivelayer 31 above the exposed transparent substrate 12 (in the repair area30B) such that a first electrode 111B of the repair microLED 11B bondsand electrically connects with the second conductive layer 31. The firstelectrode 111B and the second electrode 112B of the repair microLED 11Bare disposed at bottom and top of the repair microLED 11B, respectively.Further, as shown in FIG. 3I, which shows a cross-sectional view along across line 3B-3B′ of FIG. 4, the overlapped second conductive layer 31and the extended electrode 13B (in the repair area 30B) are welded to beelectrically connected by using, for example, laser welding technique.Accordingly, the first electrode 111B of the repair microLED 11Belectrically connects with the selection electrode 13A via the secondconductive layer 31 and the extended electrode 13B. Next, a second lightguiding layer 14B is entirely formed (FIG. 3H) to cover the repairmicroLED 11B and the common electrode 15 and the first light guidinglayer 14A in the original area 30A in order to controllably guide lightgenerated by the repair microLED 11B towards the transparent substrate12 such that the generated light may be emitted downwards and bevertical to a top surface of the transparent substrate 12.

As shown in FIG. 3J, which is similar to FIG. 3G, the second lightguiding layer 14B is etched to expose the common electrode 15 in theoriginal area 30A and the second electrode 112B of the repair microLED11B. Next, a top electrode 22 is formed above the second light guidinglayer 14B to electrically connect with the common electrode 15 in theoriginal area 30A and the second electrode 112B of the repair microLED11B. Accordingly, the top electrode 22 electrically connects with thecommon electrode 15 in the original area 30A. Therefore, the topelectrode 22 equivalently acts as a common electrode for the repairmicroLED 11B. The common electrode 15 and the top electrode 22 act toreflect the light generated by the repair microLED 11B downwards and toconfine the light generated by the repair microLED 11B to prevent thelight from leaking upwards or sidewards.

FIG. 5A to FIG. 5F show cross-sectional views illustrating a repairmethod of a (bottom emission) microLED display 400 according to a fourthembodiment of the present invention. The embodiment is adaptable to aflip-chip type microLED. Same numerals are used to denote elements thatare the same as the microLED display 200 of FIG. 2 or the microLEDdisplay 300 of FIG. 3A to FIG. 3J.

As shown in FIG. 5A, a transparent substrate 12 is provided, and abottom conductive layer 41 is formed on a top surface of the transparentsubstrate 12. The bottom conductive layer 41 may include conductivematerial such as metal. Next, a second insulating layer 16A is formedabove the bottom conductive layer 41 and the transparent substrate 12.In the embodiment, the second insulating layer 16A may be an inter-layerdielectric (ILD) layer, which may include electrically insulatingmaterial such as silicon oxide or silicon nitride.

As shown in FIG. 5B, a selection electrode 13 is formed above the secondinsulating layer 16A. In the embodiment, the selection electrode 13 maybe a first metal layer. Next, a first insulating layer 16B is formedabove the second insulating layer 16A and the selection electrode 13. Inthe embodiment, the first insulating layer 16B may be an inter-layerdielectric (ILD) layer, which may include electrically insulatingmaterial such as silicon oxide or silicon nitride.

As shown in FIG. 5C, a through hole 161 is formed in the firstinsulating layer 16B. Next, a conductive layer 17 and a common electrode15 are formed on a top surface of the first insulating layer 16B, wherethe conductive layer 17 fills the through hole 161 and thus electricallyconnects with the selection electrode 13. In the embodiment, theconductive layer 17 and the common electrode 15 may be a second metallayer.

As shown in FIG. 5D, an original microLED 11A is disposed above theconductive layer 17 and the common electrode 15 such that a firstelectrode 111A of the original microLED 11A bonds and electricallyconnects with the conductive layer 17, and a second electrode 112A bondsand electrically connects with the common electrode 15.

After the structure of FIG. 5D is formed, the original microLED 11A issubjected to functional test. If the original microLED 11A passes thetest, the process of FIG. 5F is performed; otherwise the process of FIG.5E to FIG. 5F is performed.

As shown in FIG. 5E, if the original microLED 11A fails the functionaltest, a repair microLED 11B is then disposed above the conductive layer17 and the common electrode 15 such that a first electrode 111B of therepair microLED 11B bonds and electrically connects with the conductivelayer 17 and a second electrode 112B bonds and electrically connectswith the common electrode 15. Specifically, the repair microLED 11B andthe original microLED 11A are disposed at the same level. Next, therepair microLED 11B is subjected to functional test. If the repairmicroLED 11B fails the functional test, another repair microLED 11B isdisposed, followed by functional test. This procedure repeats untilpassing the functional test. FIG. 5E exemplifies disposing four repairmicroLEDs 11B. FIG. 6 shows a partial top view illustrating the microLEDdisplay 400 of FIG. 5A to FIG. 5F. Specifically, a bottom end (or nearend) of the conductive layer 17 is near the selection electrode 13, anda top end (or far end) of the conductive layer 27 is far away from theselection electrode 13. The original microLED 11A is disposed at farends of the conductive layer 17 and the common electrode 15. If theoriginal microLED 11A fails the functional test, a repair microLED 11B_1is disposed at near ends of the conductive layer 17 and the commonelectrode 15. Before (or after) disposing the repair microLED 11B_1, ifit is found that the original microLED 11A makes shoring between theconductive layer 17 and the common electrode 15, the conductive layer 17and/or the common electrode 15 is cut off at position 171/151, forexample, by using laser cutting technique. If the repair microLED 11B_1still fails the functional test, a repair microLED 11B_2 is disposednearer the near ends of the conductive layer 17 and the common electrode15. Before (or after) disposing the repair microLED 11B_2, if it isfound that the repair microLED 11B_1 makes shoring between theconductive layer 17 and the common electrode 15, the conductive layer 17and/or the common electrode 15 is cut off at position 172/152. Otherrepair microLEDs 11B_3 and 11B_4 follow the same repair procedure asdescribed above.

As shown in FIG. 5F, a light guiding layer 14 is formed to cover thefirst insulating layer 16B, the conductive layer 17 and the commonelectrode 15 in the pixel light-emitting area, and cover the originalmicroLED 11A and/or the repair microLED 11B (only one microLED is shownin FIG. 5F) in order to controllably guide light generated by theoriginal microLED 11A and/or the repair microLED 11B towards thetransparent substrate 12 such that the generated light may be emitteddownwards and be vertical to a top surface of the transparent substrate12. Next, a reflecting layer 19 is formed above the light guiding layer14 to reflect the light generated by the original microLED 11A/repairmicroLED 11B downwards and to confine the light generated by theoriginal microLED 11A/repair microLED 11B to prevent the light fromleaking upwards or sidewards. In the embodiment, the reflecting layer 19may be a third metal layer.

Compared to the vertical-type microLED display 300 of the thirdembodiment (FIG. 3A to FIG. 3J), the flip-chip type microLED display 400of the fourth embodiment (FIG. 5A to FIG. 5F) provides a repair methodthat uses fewer layers (that is, fewer masks and process steps) andfacilitates functional test and repair.

Although specific embodiments have been illustrated and described, itwill be appreciated by those skilled in the art that variousmodifications may be made without departing from the scope of thepresent invention, which is intended to be limited solely by theappended claims.

What is claimed is:
 1. A bottom emission micro light-emitting diode(microLED) display, comprising: a transparent substrate; a microLEDdisposed above the transparent substrate, the microLED being a flip-chiptype microLED; a light guiding layer surrounding the microLED tocontrollably guide light generated by the microLED towards thetransparent substrate; a reflecting layer formed over the light guidinglayer to reflect the light generated by the microLED downwards and toconfine the light generated by the microLED to prevent the light fromleaking upwards or sidewards; a selection electrode disposed above thetransparent substrate, and electrically connected with a first electrodeof the microLED; and a common electrode disposed between the microLEDand the transparent substrate, and electrically connected with a secondelectrode of the microLED.
 2. The display of claim 1, furthercomprising: an insulating layer disposed above the transparent substrateand the selection electrode; and a conductive layer disposed above theinsulating layer, the conductive layer electrically connecting with theselection electrode; wherein a first electrode of the microLED bonds andelectrically connects with the conductive layer.
 3. The display of claim1, wherein the transparent substrate comprises glass.
 4. The display ofclaim 1, wherein the light guiding layer comprises transparent materialwith diffractive index higher than 1.4.
 5. The display of claim 1,wherein the light guiding layer comprises polymer.
 6. The display ofclaim 1, wherein the reflecting layer comprises electrically conductivematerial.
 7. The display of claim 6, wherein the reflecting layercomprises metal.